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CHAPTER 1 HISTORICAL DEVELOPMENT Theoretically, any tide anywhere can produce power in some quantity from the energy otherwise dissipated during its ebb stage, but there are relatively few locations in the world where topographical conditions are such as (1) to cause the incoming tide to rise to an unusual or abnormal height through being forced to its culminating level in a long gradually contracting channel and (2) to permit a stable barrier to be placed in the path of the tide, provided with openings to allow the tidal fl ow to pass through to its culminating level and thereafter capable of being closed to hold this level as the tide recedes on the seaward side of the barrier. Under such a condition, it follows that, as the tide recedes seaward, or ebbs, a gradually increasing head differential is created between the falling seaward levels and the fi xed level held above and within the barrier, designated the tidal basin. When this head differential has reached some predetermined value the potential energy thereby created through the agency of the tidal fl ow impounded by the barrier can be converted into con- trollable mechanical or electrical power. Thus, in addition to a suffi ciently high tidal range, at least 5 m as a rule-of-thumb for construction of an economically feasible tidal powerCOPYRIGHTED plant, the site should also MATERIAL include a natural bay with an adequate area and volume and be so situated that the operation of the plant will not signifi cantly reduce the tidal range. There are two limitations associated with the production of this tidal power. First, the power potential will vary during the approximately 12-h cycle of ebb and fl ow. Second, a similarly recurring cessation of all power production Elements of Tidal-Electric Engineering. By Robert H. Clark Copyright © 2007 the Institute of Electrical and Electronics Engineers, Inc. 1 2 HISTORICAL DEVELOPMENT during a period that begins when the rising tide, coupled with the falling head in the tidal basin, has eliminated the operable head, and ends when the tide has receded to a level resulting in the predetermined minimum operating head at which the turbine can function and with the tidal basin again full to high slack level. In principle, therefore, a simple tidal development can only produce power intermittently within the daily tidal cycles. The energy in the ebb and fl ow of the tides, particularly in those areas of the world where the tides exhibit a relatively large range, has long been recog- nized as a naturally repetitive source of energy. In fact, this source was tapped more than a millenium ago to carry out some of the more tedious tasks, such as the grinding of grains. According to historical records, inhabitants of the coastlines, particularly those bordering the North Atlantic, installed simple tidal mills on the shores of Gaul, Andalusia, and England, at least as early as the Middle Ages, to aid them in their daily work. It is likely that tidal energy also tapped in other countries, perhaps even earlier. The tidal mill is a version of the conventional water mill but required just a little extra skill and care to operate it. The dam, closing off the small bay or mill pond from the sea, was equipped with sluice gates, or fl ap gates. These opened automatically with the tidal current during the fl ood and closed during the ebb to trap the water in the mill pond. From there it was directed to drive a large-diameter, wooden paddle wheel and thence back to the sea. A schematic arrangement is shown in Fig. 1.1. These ancient mills used the ebb tide for the generating cycle, and the engineering skill of those who built them is to be admired. The great driving wheels, made of wood and subsequently of cast iron, mostly with replaceable wooden teeth, matched exactly the smaller wheels that they operated. Many mills were automated to the extent that they could be operated by one person who had readily available a series of ropes and pulleys by which any part of the mill’s machinery could be set in motion. Since the tidal cycle and solar cycle are out of phase in most locations around the world, the miller had to mill when the tide was right whether at midnight or midday—an early example of fl exible working hours! The earliest records of tidal mills date from about the eleventh century. For the next several centuries, many tidal mills were reported to have been in operation along the Atlantic coast of Europe, mostly in the British Isles, Wheel Sluices Figure 1.1 Typical tidal mill setup. HISTORICAL DEVELOPMENT 3 France, and Spain. One such installation in the Deben Estuary (England) was mentioned as early as 1170 in the records of the Parish of Woodbridge. The present building there (Fig. 1.2) dates from the eighteenth century, and the mill was in operation until 1957 when the main wheel shaft broke. Since then, the mill pond has been converted into a yacht marina and the mill restored as a museum piece. Two tidal mills were still in operation in the Rance Estuary (Fig. 1.3) when Electricité de France began work leading to the construction of the world’s fi rst large, modern tidal-electric power plant. Tidal energy was tapped as early as 1617 in North America. Slade’s Mill in Chelsea, Massachusetts, built about 1734 to grind spices and developed about 35 kW. Prior to 1800, at least two small, single-basin tidal mills were in existence in Passamaquoddy Bay. Also according to Bernstein (1965), there were tidal mills in Russia as early as the eighteenth century. Besides the use of the simple water wheel turned by the tide and connected by belts or gears to grinding or mill stones, relatively primitive devices were developed to harness the tidal energy for other uses, such as for pumping. Even in 1824, part of the water supply of London was still provided by 6-m diameter water wheels installed in 1580 under the arches of London Bridge. Some of these structures for transforming tidal energy were of impressive size. Figure 1.2 Tidal mill on the Deben Estuary. (Courtesy Woodbridge Tide Mill Trust.) 4 HISTORICAL DEVELOPMENT Figure 1.3 Tidal mill in the Rance Estuary. (Courtesy of Electricité de France.) A tidal mill built at the beginning of the eighteenth century on the shores of Rhode Island, United States, had 3.36-m diameter wheels that were 7.92 m in width and weighed about 20 tons. Many ingenious methods, in addition to the water wheel, were devised to use the potential energy of the tides or the kinetic energy of the tidal cur- rents, or combinations of both, by means of such devices as lifted platforms or weights and air compressors. At least 300 patents have been registered during the past 100 years for different technical systems to extract the energy of the tides. However, all of these earlier methods had one common characteristic— they were devised to transform the energy of the tides into mechanical energy for local consumption. An interesting survey, with an extensive bibliography, of the development and use of tidal power from classical times up to the completion of La Rance (France) tidal-electric plant in 1967 is presented by Charlier (1969). The early tidal developments could extract only an infi nitesimally small fraction of the potentially available energy, producing, perhaps, the equivalent of up to 75 kW for use at the site. Such micro amounts of power served the needs of the community before the advent of the electric motor and long- distance power transmission. Efforts to rationalize tidal power technology were undertaken centuries ago. A handbook for the construction of tidal mills was written by an Italian, HISTORICAL DEVELOPMENT 5 Mariano, in the fi fteenth century. At the beginning of the eighteenth century, a Frenchman, Belidor, considered the “quality” of tidal energy. In his treatise on hydraulic architecture, he stated principles for multibasin operation to achieve a continuous output of energy. The advent of the Industrial Revolution introduced insatiable demands for power and energy on a large scale. The exploitation of tidal energy fell into disuse because hydroelectric development of rivers and fossil-fi red power plants offered easier technological access to power generation on an industrial scale. The advances in technology for the development of these latter sources of power resulted in neglect of tidal power technology. The small tidal mills, not being able to meet the competition, disappeared from the scene—monu- ments of a technology that had outlived its day. During the past four decades there have been a number of major advances in technology, notably in hydraulic turbogenerating units, in marine construction, and in the mathematical understanding of tidal cycle variations. It is now clear that the major technological problems formerly associated with large- scale tidal power developments have been resolved. It has only been since the 1960s that the construction of modern tidal- electric stations has been attempted. On November 26, 1966, the fi rst large- scale, modern, tidal-electric plant went into operation in La Rance Estuary near St. Malo, France. Less than a year later, the plant was fully equiped with 24– 10,000 kW turbogenerators and has been operating successfully since that time as an integral part of the electrical utility system of Electricité de France. During the latter part of 1968, an experimental tidal power plant com- menced operation at the mouth of Kislaya Gulf near Murmansk, Russia, on the coast of the Barents Sea.

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